优先级队列的使用

自定义对象，并实现Comparable接口。使用代码如下：

package tijava.container;

import java.util.Collections;
import java.util.PriorityQueue;
import java.util.Queue;

class ToDoItem implements Comparable<ToDoItem> {
	private char primary;
	private int secondary;
	private String item;

	public ToDoItem(char primary, int secondary, String item) {
		super();
		this.primary = primary;
		this.secondary = secondary;
		this.item = item;
	}

	@Override
	public int compareTo(ToDoItem o) {
		if (this.primary > o.primary)
			return +1;
		if (this.primary == o.primary) {
			if (this.secondary > o.secondary)
				return +1;
			else if (this.secondary == o.secondary)
				return 0;
		}
		return -1;
	}

	public String toString() {
		return Character.toString(primary) + this.secondary + " : " + this.item;
	}
}

public class PriorityQueueDemo {
	public static void main(String[] args) {
		Queue<ToDoItem> q = new PriorityQueue<ToDoItem>();
		q.add(new ToDoItem('C', 4, "Empty trash"));
		q.add(new ToDoItem('A', 2, "Feed dog"));
		q.add(new ToDoItem('B', 7, "Feed bird"));
		q.add(new ToDoItem('C', 3, "Mow lawn"));
		q.add(new ToDoItem('A', 1, "Water lawn"));
		q.add(new ToDoItem('B', 1, "Feed cat"));

		while (!q.isEmpty()) {
			System.out.println(q.remove());
		}
		
		//reverseOrder
		Queue<ToDoItem> q1 = new PriorityQueue<ToDoItem>(1,
				Collections.reverseOrder());
		q1.add(new ToDoItem('C', 4, "Empty trash"));
		q1.add(new ToDoItem('A', 2, "Feed dog"));
		q1.add(new ToDoItem('B', 7, "Feed bird"));
		q1.add(new ToDoItem('C', 3, "Mow lawn"));
		q1.add(new ToDoItem('A', 1, "Water lawn"));
		q1.add(new ToDoItem('B', 1, "Feed cat"));

		while (!q1.isEmpty()) {
			System.out.println(q1.remove());
		}
	}
}

output:

A1 : Water lawn
A2 : Feed dog
B1 : Feed cat
B7 : Feed bird
C3 : Mow lawn
C4 : Empty trash
C4 : Empty trash
C3 : Mow lawn
B7 : Feed bird
B1 : Feed cat
A2 : Feed dog
A1 : Water lawn